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Task 15. Use the words and word combinations in the box to complete the text. Use each word only once.
Point-to-point positioning can be performed in single-1) ________ or multiaxis systems with servomotors in closed loops or stepping motors in 2) ________ loops. X- Y tables and milling machines position their loads by multi-axis point-to-point control. Sequencing control is the control of such functions as opening and 3) ________ valves in a preset sequence or starting and stopping a conveyor 4) ________ at specified stations in a specific order. Speed control is the control of the velocity of the motor or actuator in a 5) ________ . Torque control is the control of motor or actuator current so that torque remains constant despite load changes. Incremental motion control is the simultaneous control of two or more 6) ________ such as load location, motor speed, or torque.
Task 16. Watch the video file “Motion Control System Overview” and write an essay (100-120 words) on the topic “If I were a head of Metal Manufacturing Company (MMC) I would…”. Use information below if necessary.
Task 17. Watch the video file “What Is a Servomotor”. Write a short review (100 words) on servomotors. Use the information below.
Basically, the hallmark of any servomotor is the presence of feedback and closed-loop control. Servomotors are able to provide precise control of torque, speed or position using closed-loop feedback. They can also operate at zero speed while maintaining enough torque to maintain a load in a given position. Servomotors have several distinct advantages over other types of motors. For starters, they offer more precise control of motion. This means they can accommodate complex motion patterns and profiles more readily. Also, because the level of precision offered is high, the position error is greatly reduced.
UNIT 6. TOOL WEAR AND SHARPENING
Task 1. What do you know about the history of industrialization? Name the most important scientists in the field of engineering and describe their inventions.
Task 2. Look at these pictures. Try to compare them and discus the problem of industrial modernization and automation.
Task 3. Read the text and translate all underlined words into Ukrainian.
Metal cutting tools wear constantly when they are being used. A normal amount of wear should not be a cause for concern until the size of the worn region has reached the point where the tool should be replaced. Normal wear cannot be avoided and should be differentiated from abnormal tool breakage or excessively fast wear. Tool breakage and an excessive rate of wear indicate that the tool is not operating correctly and steps should be taken to correct this situation.
There are several basic mechanisms that cause tool wear. It is generally understood that tools wear as a result of abrasion which is caused by hard particles of work material plowing over the surface of the tool. Wear is also caused by diffusion or alloying between the work material and the tool material. In regions where the conditions of contact are favorable, the work material reacts with the tool material causing an attrition of the tool material.
The rate of this attrition is dependent upon the temperature in the region of contact and the reactivity of the tool and the work materials with each other. Diffusion or alloying also occurs where particles of the work material are welded to the surface of the tool. These welded deposits are often quite visible in the form of a built-up edge, as particles or a layer of work material inside a crater or as small mounds attached to the face of the tool.
Among the other mechanisms that can cause tool wear are severe thermal gradients and thermal shocks, which cause cracks to form near the cutting edge, ultimately leading to tool failure. This condition can be caused by improper tool grinding procedures, heavy interrupted cuts, or by the improper application of cutting fluids when machining at high cutting speeds. Chemical reactions between the active constituents in some cutting fluids sometimes accelerate the rate of tool wear.
The wear mechanisms described bring about visible manifestations of wear on the tool which should be understood so that the proper corrective measures can be taken, when required.
Flank Wear: Tool wear occurring on the flank of the tool below the cutting edge is called flank wear. Flank wear always takes place and cannot be avoided. It should not give rise to concern unless the rate of flank wear is too fast or the flank wear land becomes too large in size. The size of the flank wear can be measured as the distance between the top of the cutting edge and the bottom of the flank wear land.
Cratering: A deep crater will sometimes form on the face of the tool which is easily recognizable. The crater forms at a short distance behind the side cutting edge leaving a small shelf between the cutting edge and the edge of the crater. This shelf is sometimes covered with the built-up edge and at other times it is uncovered. Sometimes cratering cannot be avoided and a slow increase in the size of the crater is considered normal.
Cutting Edge Chipping: Small chips are sometimes broken from the cutting edge which accelerates tool wear but does not necessarily cause immediate tool failure. Chipping can be recognized by the appearance of the cutting edge and the flank wear land. A sharp depression in the lower edge of the wear land is a sign of chipping and if this edge of the wear land has a jagged appearance it indicates that a large amount of chipping has taken place.
Deformation: Deformation occurs on carbide cutting tools when taking a very heavy cut using a slow cutting speed and a high feed rate. A large section of the cutting edge then becomes very hot and the heavy cutting pressure compresses the nose of the cutting edge, thereby lowering the face of the tool in the area of the nose. This reduces the relief under the nose, increases the width of the wear land in this region, and shortens the tool life.
Surface Finish: The finish on the machined surface does not necessarily indicate poor cutting tool performance unless there is a rapid deterioration. The principal cause of a poor surface finish is the built-up edge which forms along the edge of the cutting tool. The most effective way to eliminate the built-up edge is to increase the cutting speed. When the cutting speed is increased beyond a certain critical cutting speed, there will be a rather sudden and large improvement in the surface finish.
Cutting tool materials that do not alloy readily with the work material are also effective in obtaining an improved surface finish. Straight titanium carbide and diamond are the two principal tool materials that fall into this category.
Task 4. Answer the following questions:
1. What is tool wear?
2. What does an excessive rate of wear indicate?
3. How can temperature influence tool wear?
4. What basic mechanisms that cause tool wear can you name?
5. From time to time cratering cannot be avoided and a slow increase in the size of the crater is considered normal, isn`t it?
6. How can chipping be recognized?
7. When does deformation occur?
8. How to eliminate the built-up edge of a tool?
Task 5. Decide whether the following statements are true or false:
1. An excessive rate of wear indicates that the tool is not operating correctly and it should be corrected.
2. Wear is caused only by alloying between the work material and the tool material.
3. Where the conditions of contact are favorable, the work material reacts with the tool material causing an accelerationof the tool material.
4. The rate of attrition is dependent upon the temperature in the region of contact and the reactivity of the tool and the work materials with each other.
5. Chemical reactions between the active constituents in cutting fluids accelerate the rate of tool wear at all.
6. Flank wear is a tool wear occurring on the flank of the tool below the cutting edge.
7. Often cratering cannot be avoided and a slow increase in the size of the crater is considered quite normal.
8. Chipping can be increased by the appearance of the cutting edge.
9. The principal cause of a poor surface finish is the built-up edge which forms along the edge of the cutting tool.
10. The most effective way to eliminate the built-up edge is to decrease the cutting speed.
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